Testing the Discovery of Archean Terrestrial Mass-independent Sulfur Isotope Anomalies

本提案的主要目标是通过重复分析来确认与质量无关的硫同位素分馏的发现，以验证准确性，并识别异常硫的矿物宿主和测量其非均质性。对硫同位素分析进行额外研究的动机是因为它们在古代岩石中作为生物标志物的实用性。在前寒武纪岩石中，化石不存在，有机残留物已转化为碳，硫同位素质量相关分馏仍然是硫酸盐还原微生物生命过程的不可磨灭的记录。随着与质量无关的硫同位素分馏在太古代岩石中的发现，硫同位素地球化学的意义更加突出。这种分馏在高层大气中是已知的，其中气相反应在紫外光的强烈影响下发生。因此，硫同位素分析可能为以前的生命存在提供证据，但它们也可能记录了地球大气演化中以前未知的一章。本文将探讨太古代和元古代变质岩中异常硫的地理分布。将测量地层剖面以建立硫同位素分馏时间分布。卡内基研究所地球物理实验室的新硫同位素激光微探针将用于对太古代和元古代变质岩进行详细检查。

AbstractEAR-0125096RumbleCarnegie Institution of Washington, Geophysical LaboratoryThe primary goal of this proposal is to confirm the discovery of mass-independent sulfur isotope fractionation by replicate analyses to validate accuracy and to identify mineral hosts of anomalous sulfur and measure its heterogeneity. The motivation for additional study of sulfur isotope analyses is because of their utility as biomarkers in ancient rocks. In Precambrian rocks where fossils are non-existent and organic residues have been converted to carbon, sulfur isotope mass-dependent fractionations remain as an indelible record of the vital processes of sulfate-reducing microbes. With the discovery of mass-independent sulfur isotope fractionations in Archean rocks, sulfur isotope geochemistry has acquired even greater significance. Such fractionations are known in the upper atmosphere where gas phase reactions take place under the strong influence of ultraviolet light. Sulfur isotope analyses, therefore, may give evidence for the former existence of life but they may also record a previously unknown chapter in the evolution of Earth's atmosphere. This proposal will examine the distribution of anomalous sulfur geographically in Archean and Proterozoic metamorphic rocks. Stratigraphic sections will be measured to establish a sulfur isotope fractionation time distribution. The new sulfur isotope laser fluorination microprobe at the Geophysical Laboratory of the Carnegie Institution will be used to do detailed examination of Archean and Proterozoic metamorphic rocks.